Preserve special trailing ":" in MANPATH
A trailing : in MANPATH is used to represent the standard search path, but LbEnv (xenv, actually) removes it (which is a perfectly sensible action fo PATH, LD_LIBRARY_PATH, etc).
A trailing : in MANPATH is used to represent the standard search path, but LbEnv (xenv, actually) removes it (which is a perfectly sensible action fo PATH, LD_LIBRARY_PATH, etc).